O2 should be very low on the list. At the altitude he was flying 14-16K it will mostly give you a headache. Even at 18K, you not going to pass out, especially not someone in physical shape to be able to hike up a mountain and fly a paraglider.
I often see O2 and dehydration high on the list of possible causes, as if you suddenly pass out if you don’t start using O2 at 10K or drink few gallons of water.
I am not going to speculate but there can be many reasons higher on the list.

Ramy